1. Field of the Invention
This invention relates to a start circuit for an automatic telephone answering device, which distinguishes between a bell signal and crosstalk noise, such as a dial signal.
2. Description of the Prior Art
Conventional start circuits operate by rectifying an incoming telephone line signal, integrating the rectified signal by applying it to a capacitor, and operating a switching circuit, e.g. a Schmitt trigger, when the capacitor voltage exceeds a predetermined level. Circuits of this type frequently and erroneously respond to extraneous noise signals on the line, such as dial signals, however, since they are unable to distinguish between bell and dial signals.